Powering lm317 driver with a 12v 1a wallwort?

[extremeodd]

Well I have a couple of labby style lasers Ive built that are fairly lower power, the strongest one only pulls about 3-400ma. Ive been using a 9v battery but that dies pretty quickly so I was digging around in my drawers and found a couple of 12v wallwork transformers. One is rated for 600ma and one is 1a, I was wondering if this would work fine with the lm317 driver Im using. I plan on cutting off the round adapter, plugging it in and using my multimeter to figure out which is positive and which is negative then attaching it to a 9v pigtail so I dont have to mess with the wiring in the laser. Also that way I can go to a portable 9v if I wish. Are there any problems with my reasoning? I realize there will be a bit more heat from the lm317 at 12v but it barely gets warm as is so Im not worried.

 

[Cyparagon]

Yes, that will work fine. It is a good idea to add a filtering cap if you haven't already.

 

[extremeodd]

Well I tried it earlier, put a cap on it and my diode went pop. Thankfully I tried it on my loc diode so itll be cheap to replace. It lit up for about .5 sec and nothing, not even led just nothing. I think it might of been too high of a turn on voltage (15v without a load on it), but who knows.

 

[Flaminpyro]

What was the cap that poped rated voltage ? and could you of hooked the cap up backwards ? that will pop them right off.

 

[extremeodd]

well I made sure to check the caps + and - (its marked on the cap). I believe the cap is 35v rated. I tried going back to the 9v battery and still nothing. When these diodes pop do they always LED or can they go completely dark?

 

[Flaminpyro]

They usuly LED but they can go dead with NO output what so ever.
you should be able to do what you are trying, set it back up again
and use something else for a load at first even a car tail light.

 

[extremeodd]

Well I could try setting it up again but I know the lpc-815 diode is dead. I hooked it back up the way it was before with a 9v and nothing. I do have another "labby" type with a sf-aw210 but I hear they can be quite sensitive, and that one was $16 vs $9 for the red. So Ill just stick to the 9v battery until I get some 14500s or a variable power supply.

 

[Cyparagon]

I meant a cap on the input side since electrically speaking, wall warts are often pretty noisy.

A cap on the output is recommended no matter the source. You need to be sure to short them before putting them in though.

 

[Benm]

Wallwarts are always a bit dangerous. I recommend testing their actual output voltage with a multimeter before using them to power anything. There are good ones, but i've seen 12 volt models that put out 20 volts or more when not or slightly loaded.

Your LD driver should still be able to compensate for all that, but you should consider the amount of heatsinking required. Also, input caps on your driver should have voltage ratings well above the advertised voltage on the wallwart supply (i'd consider double to be on the safe side).

 

[midias]

Wall warts often have nasty ripple on the output so always make sure to use a decent filter cap on the front end at least 100uf and a smaller filter cap 1 or .1 uf

 

[3zuli]

well, LM317 is up to 35V so there's no problem with voltage. however you MUST use some bigger heatsink for LM317, at >350mA and 12V it heats up VERY quickly

 

[extremeodd]

Well I guess my 10uf was a bit small, Im sure I have a 1 farad audio cap around here somewhere :crackup:. Well I may order several diodes since they come quite cheaply, and having a backup incase the wallwart blows up another one. Ill grab a few more larger caps from radioshack.

 

[GBD]

hmm,

Also, some wallwarts have more terrible ripple then the others.
I found a traditional 60Hz transformer and rectifier wall warts are generally completly unfiltered on thier output, however thier lighter, solid state counter parts (Switch mode) generally already have some filter capacitance on the output.

SMPS style wall warts also operate at higher frequencies (several KHz) rather then just a 60Hz output of a standard iron core transformer.

long story short, if your wall wart is of the 60Hz iron core variety, you will need some very hefty filter capacitance (1000uF+) if you want to smoothen out the fullwave DC output, also, adding zeners or TVS diodes (you can even use MOVs on the AC output) will greatly help to stop spikes and transients in line.)

Same can be done for SMPS style supplies, although due to the higher operating frequency, usually you do not need as high filter capacitance. (around 100uF will be enough).

You will still have noise and spikes from either supply topology, just the switchmode ones are easier to manage IMO, with some good regulation and filtering (as well as spike supression devices)

Hope that helps a bit.

 

[extremeodd]

Wow, that completely explains why the diode done went pop. I guess Ill save up and get a good variable powersupply.

 

[Juniortore1]

I made 2 lm317 drivers now, both duds. I had one here, I was inputting 12 volts, with 4,700uF smoothing. I had a nice 25 turn, 20 ohm trimpot to adjust power, a 1n4001 diode and capacitor on the out as the schematic said. I hooked it up to my LPC-815, for it to make a dim red glow at 50ma, so I cranked it up, and it didnt really get any brighter at 130ma, and then it died. I was kinda mad, but figured I touched the inside of the LPC when harvesting. So, I stuck in a 16x red, for it to do the same thing, but die at 70 ma.

I now made another lm317 driver, and spent two hours into making it nice and compact. It has 4 paralleled 1/4w 10 ohm resistors for 3 ohms for about 400ma to go to a lpc-815 I will soon get. I had a 20 ohm trimpot in series with the makeshift 3 ohm. I wired it up to a dummy load, for NO output in any form. Same 12v

Im kinda pissed, all of my homemade lasers have been a fucking fail. I still refuse to give up, but man, thats a lot of money in the trash.

 

[GBD]

Most likly culprit is overvoltage. 12 volts is way too much for that linear regulator (assuming you are using the exact original LM317 circuit I see so often around here), sure it has a high voltage drop, but not enough for a red. IIRC they have a forward voltage of 2.5V-3V.
Id suggest you either lower your voltage input, or add a dropping resistor for your supply (with the respective wattage). either that, or take another LM317 and set it up as a voltage regulator and adjust it likewise. (to feed the other LM set up as a current regulator)